cc: Report only on active tiles in tracing.

cc/layers/picture_layer_impl.h

Index: cc/layers/picture_layer_impl.h
diff --git a/cc/layers/picture_layer_impl.h b/cc/layers/picture_layer_impl.h
index f9845be9d63d798ba9d2f0bede1f93f07d040c92..47d881dfdee8118f50177f9aa1e669a147bd32e7 100644
--- a/cc/layers/picture_layer_impl.h
+++ b/cc/layers/picture_layer_impl.h
@@ -5,6 +5,7 @@
 #ifndef CC_LAYERS_PICTURE_LAYER_IMPL_H_
 #define CC_LAYERS_PICTURE_LAYER_IMPL_H_
 
+#include <set>
 #include <string>
 #include <vector>
 
@@ -191,6 +192,8 @@ class CC_EXPORT PictureLayerImpl
 
   virtual void GetDebugBorderProperties(
       SkColor* color, float* width) const OVERRIDE;
+  virtual void GetAllTilesForTracing(
+      std::set<const Tile*>* tiles) const OVERRIDE;
   virtual void AsValueInto(base::debug::TracedValue* dict) const OVERRIDE;
 
   virtual void UpdateIdealScales();